Position detection and control devices

ABSTRACT

Apparatus for monitoring relative movement of a member, which includes an extended diffraction grating, a plurality of cooperating index gratings, at least one source of cyclically modulated radiation and photo-electric transducer means arranged so that the extended grating is mounted on the movable machine part and cyclically modulated radiation passes through the extended grating and the fixed index gratings to the photoelectric transducer means so as to produce therefrom, through the moire fringe effect, a cyclic electrical signal which is constant in phase while the member is stationary and varies in phase in accordance with movement of the member.

[ July 24, 1973 POSITION DETECTION AND CONTROL DEVICES [75] Inventor:Alexander Russell, East Kilbride,

Glasgow, Scotland [22] Filed: Dec. 21, 1971 I [21] Appl. No.: 210,332

[52] U.S. Cl 250/231 R, 250/237 G, 318/560 [51] Int. Cl. G0ld 5/34 [58]Field of Search 250/208, 209, 237 G,

[56] References Cited UNITED STATES PATENTS 2,886,718 5/1959 Shepherd etal. 250/220 R 3,227,888 1/1966 Shepherd et a1. 250/237 G 3,351,76811/1967 Cooke 250/237 G 3,500,055 3/1970 Russell et a1 356/167 X PrimaryExaminer-Walter Stolwein Attorney-Gordon W. Daisley [57] ABSTRACTApparatus for monitoring relative movement of a member, which includesan extended diffraction grating, a plurality of cooperating indexgratings, at least one source of cyclically modulated radiation andphotoelectric transducer means arranged so that the extended grating ismounted on the movable machine part and cyclically modulated radiationpasses through the extended grating and the fixed index gratings to thephoto-electric transducer means so as to produce therefrom, through themoire fringe effect, a cyclic electrical signal which is constant inphase while the member is stationary and varies in phase in accordancewith movement of the member.

11 Claims, 6 Drawing Figures PAIENInJuL24|92a SHEET 2 or 3 osclLLAT oRl2\ P2 DELAY/54 Y PHOTODIODE 7O 76 7L 66 72 78 36 4 i r fireyi 62PHOTODIODE FIG. 3.

PATENTEBJULZMQTS SHEET 3 UF 3 REVOLUTION SENSER FIG.

POSITION DETECTION AND CONTROL DEVICES This invention relates toposition detection and control devices suitable for use with e.g.precision machines or apparatus such as machine tools.

It is well known to utilize moire fringes produced by two opticalgratings arranged with an angle between the grating lines and attachedto a fixed and a moving member of, for example, a machine tool, as partof a position measuring system. It is also known to use coarse gratingsin conjunction with an interpolation system to give a high-resolutionmeasuring system, such as observation of a fringe at four pointsfollowed by integration to give a sine wave for comparison with a mastersine wave. In previous systems of conventional kind, any change of phaserequired was brought about by means of mechanical moving parts, havingthe disadvantages of complication and the introduction of vibration.

According to the invention a time-phase transducer comprises an extendeddiffraction grating, a set of at least two index diffraction gratingseach of which can coact with part of said extended grating to produce anindividual moire fringe pattern, the extended grating and the set ofgratings being capable of relative movement, a source of cyclicallymodulated radiation of a given frequency which can illuminate theaforesaid gratings to produce the individual moire fringe patterns,either the radiation source producing a plurality of radiations of saidgiven frequency but of different individual phases for each individualindex grating and/or each index grating having an individual phaserelationship with the extended grating whereby the resulting outputarising from each index grating is a plurality of cyclically modulatedbeams of radiation bearing moire fringe patterns which differ in phasein a cyclically symmetrical manner, photo-electric transducer means forreceiving the resulting outputs arising from each index grating andcombining them to produce at least one cyclically modulated outputsignal which in consequence varies in phase in accordance with anyrelative movement between the extended grating and the set of indexgratings.

According to an optional feature of the invention one radiation sourceproduced a single modulated radiation and n index gratings (where n isat least 3) are provided, arranged so that the moire fringe patternsdiffer from one another in spatial phase by a whole multiple of In of360. Preferably four index gratings are provided, differing in spatialphase by 90 or multiples thereof, four photo-electric cells forreceiving the outputs from each index grating, and a phase shiftingcircuit to which the photo-electric cells are connected in inverseparallel and which imposes a relative phase shift of 90 on one inputcompared with that imposed on the other input so as to produce an outputtherefrom which contains the modulation frequency of the radiationsource and varies in phase with relative movement between the extendedgrating and the index gratings; the phase shifting circuit beingdesirably a resistancecapacitance circuit.

According to a further optional feature of the invention n radiationsources are provided, where n is at least 3, a corresponding number ofindex gratings and photoelc ctric cells, and oscillator means arrangedto modulate the outputs of the radiation sources so that they differfrom one another in time-phase by whole multiples of In of 360.Preferably signal output means are provided which comprise a summingcircuit, to the input of which the outputs of the photo-electrictransducer means are connected so that the output of the signal outputmeans has substantially the same frequency as the modulation and variesin phase with rela tive movement between the extended grating and theset of index gratings.

According to another optional feature of the invention thephoto-electric transducer means has a single photo-electric cell andfocusing means intermediate the set of index gratings and thephoto-electric cell arranged so that any resulting output arising fromeach of the gratings in the set of gratings is focused onto thephoto-electric cell with the result that the output of thephoto-electric transducer means has substantially the same frequency asthe modulation of the radiation source and varies in phase with relativemovement between the extended grating and the set of index gratings.

According to yet another optional feature of the invention asynchro-resolver, a phase-sensitive detector, a servo-motor and arevolution counter are arranged so that any cyclically modulated outputsignal is fed to the stator of the synchro-resolver, any resultingelectrical output signal from the rotor of the synchro-resolver is fedto the phase-sensitive detector and is compared therein with a referencesignal derived from the modulation waveform of the radiation source, anyerrorsignal output from the phase-sensitive detector is fed to theservo-motor, which thereupon drives the rotor of the synchro-resolver soas to reduce the electrical output signal thereform towards zero, andthe revolution counter records any rotary movement of the rotor of thesynchro-resolver. Preferably a servo-amplifier is provided in which anyerror-signal output from the phase-sensitive detector is amplified bysaid servoamplifier before being fed to the servo-motor.

According to a further optional feature of the invention the serve-motoris arranged so as to drive the rotor of the synehro-resolver through agear box so that the ratio between the revolutions made by theservo-motor and the revolutions made by the rotor of the synchroresolveris the gear box ratio.

According to yet a further optional feature of the in vention theextended diffraction grating is a reflection grating and the source ofcyclically modulated radiation, index gratings and photo-electrictransducer means are arranged and adapted so as to cooperate therewith.

The term extended grating is to be understood in this specification tomean a grating the dimension of which in a direction substantially atright angles to the grating lines is large compared with the dimensionin the same direction of any of the index gratings; and the extendedgrating may, for example, be linear, annular, or may be arrangedcircumferentially upon a cylinder.

When using an optical grating as a measurement or control system elementthere are several advantages to be gained by using a time-phase mode inaccordance with the present invention where the grating spatial angle ismade to generate an output time-phase signal 1),, where it takes theform That is, the output signal is a constant amplitude signal Sin wtwhich lags a reference carrier sin wt by an amount in time equal to thetransducer angle (1).

The main advantages over a DC amplitude system are:

I. Amplitude variations do not cause errors.

2. Harmonic distortions can be removed by filtering.

3. DC drift does not cause errors.

4. The signal is compatible with other transducers such as the resolverand the inductosyn (registered trade mark).

The invention will be further described with reference to the drawingsin which:

FIG. 1 illustrates diagrammatically a first embodiment of the invention,

FIG. 2 illustrates diagrammatically an arrangement of index diffractiongratings for use in said embodiment,

FIG. 3 illustrates diagrammatically a second embodiment and FIG. 4illustrates diagrammatically a third embodiment, and with reference tothe drawings filed herewith in which FIG. 5 illustrates diagrammaticallya modification of the embodiment illustrated in FIG. 1 and FIG. 6illustrates diagrammatically an application of the invention.

In the arrangement shown in FIG. 1, one gallium arsenide lamp 10 ismodulated from oscillator means 12 and a single collimating lens 14provides light over an area suitable for four index gratings l6, 18, 20,22 and corresponding photodiodes 28, 30, 32, 34. The index grating andphotodiodes are best arranged in a square formation to make best use ofthe circular lens 14 as illustrated in FIG. 2. The index gratings eoaetwith a linear grating a portion of which is depicted at 24 and which canbe moved relative to them, mounted on a moveable part, as indicated bythe double arrow 26.

The waveforms due to the shutter actions at the linear grating/indexgrating junction are at 0, 90, 180 and 270 with respect to one anotherin spatial phase; index grating 16 corresponding to 0, 18 to 90, 20 to180 and 22 to 270.

The actual waveforms at the four cells are multiples of the lamp signaland the individual index signals and can be modified by any movement ofthe linear grating 24.

The photodiodes 28, 30, 32, 34 are connected to the amplifying means 36.The latter comprises two similar ac amplifiers 38, 40, a circuitcomprising a capacitor 42 of capacitance C and a resistor 44 ofresistance R, and an output connection 46. The photodiodes are connectedto the amplifiers, as shown, in inverse parallel, permitting algebraicsummation of the signals received by the photodiodes from the radiationsource 10 through the linear grating and the index gratings. Thecapacitance C is chosen such that its reactance Xc at the modulationfrequency is equal to the resistance R; the output produced atconnection 46 is then of the form cos(wt if the modulation of theradiation source is of the form sinwt, the phase angle being introducedby the spatial relation between the linear grating 24 and the indexgratings 16, 18, 20, 22.

In the embodiment illustrated in FIG. 3 three lamps 48, 50, 52 areprovided. These are modulated by oscillator means 12 and delay devices54, 56 so that the modulation wave forms differ in time phase by 120;that is to say if the modulation of lamp 48 is proportional to sinwt,that of 50 is proportional to sin (mt I20) and that of 52 to sin (wt240). Modulated light passes from the lamps through respectivecollimating lenses 58, 60, 62, through grating 24, through respectiveindex gratings 64, 66, 68 to respective photodiodes 70, 72, 74.Resultant output signals produced by the photodiodes are fed throughrespective capacitors 76, 78, to the amplifying means 36, which in thisem bodiment is a summing amplifier of conventional kind. Suitableselection of time constants, by conventional methods, allows lowfrequency components of the signals fed to the amplifier to be rejectedand the output from connections 46 has then the form cos (wt (b) wheremt corresponds to the modulation and 4: is the phase angle introduced bythe spatial relation between the linear grating 24 and the indexgratings 64, 66, 68.

The embodiment illustrated by FIG. 4 represents a further modification.The arrangements illustrated to the left ofline XX in FIG. 4 are thesame as those referenced similarly in FIG. 3. Instead of, as in theformer embodiments, the modulated light passing from each lamp, throughthe diffraction gratings, to corresponding individual photodiodes, allthe modulated light is collected by an imaging lens 82 and is focusedthereby on to a single photodiode 84. The signal from the photodiode isfed through capacitor 86 to amplifying means 36, the summation beingperformed by the diode instead of by the amplifying means as in theformer embodiment. The output from connections 46 of the amplifyingmeans is then again sinusoidal, dependant upon the quantities wt,corresponding to the modulation, and 4) the phase angle introduced bythe spatial relation between the linear grating 24 and the indexgratings 64, 66, 68.

Suitable modulation frequencies are between 1 and 3 KHZ but lower orhigher frequencies can be employed. Although in the embodimentsdescribed, transmission diffraction gratings have been illustrated it isequally possible, by a further modification, to use reflection gratings.The gratings which may be used range from coarse, lines per inch or lessto fine, 1,000 lines per inch or more according to the nature of thedevice which is being controlled or monitored and the work it has toperform.

An arrangement of index gratings mutually phased as described above withreference to FIG. 2 is available commercially, thus making the firstembodiment described (FIG. 1) particularly advantageous if a compactconstruction is required. This can further be achieved by the use ofintegrated circuit amplifiers.

A modification which permits an economy in manufacture is illustrated inFIG. 5. The outputs from the photodiodes 28 and 32, 30 and 34 are takenin inverse parallel direct to capacitor 42 and resistor 44 respectively.A signal from the junction of 42 and 44 is fed through a high passfilter 88 to the single AC amplifier 90. The output of the amplifyingmeans 36, produced at connections 46, is then, as before, of the formcos (wt 4)) if the modulation of the radiation source 10 is of the formsinwt.

A particular application of the invention is illustrated in a highlydiagrammatic form in FIG. 6.

In FIG. 6, references which are the same as in FIG. 1 indicate the sameintegers having the same functions, but the conventionally illustratedcircuit connections have been further simplified. Given the arrangementof reference gratings in the transducer set out above in the descriptionof the embodiment of FIG. 1, the output signals from the amplifiers canbe regarded as equivalent to resolver signals, of the form sinmt sin qband sinmt cos d:

The output signals from the amplifiers are passed through high-passfilters 92 and 94 which remove any direct voltages and low frequencies.After filtering the signals are fed to the stator windings of a synchroresolver 96, the electrical output from the rotor of the synchroresolver being connected to a phase-sensitive detector 100, and thereincompared with the modulation of the radiation source as reference. Anydifference between the rotor angle and the electrical angles sin (b, cos4) corresponding to the signals fed to the stator of 96 will give riseto an error-signal output from the phase-sensitive detector 100, whichoutput, amplified by amplifier 102, actuates the servo-motor 104. Themotor 104 is arranged so as to drive the rotor of synchro-resolver 96,through a mechanical connection 98, in such a sense that theerror-signal output from detector 100 is reduced, the resolver rotorbeing driven until the resolver output is zero. Thus for any givenposition of the transducer the servo loop comprising components 96, 100,102, 104, 98, 96 will be nulled and any subsequent movement of thetransducer will cause the servo-motor to follow the transducer outputsignals in synchronism, one revolution of the servo-motor and of therotor of the resolver taking place for every move ment of the grating 24through one grating pitch. A revolution counter 97 driven from themechanical connection 98 counts the revolutions of the rotor ofsynchroresolver 96 and can be arranged so as to interpolate fractions ofa cycle of the grating pitch.

- If a gear box, represented diagrammatically at 106, having a gearratio mm, is introduced into the mechanical connection 98, then forevery n revolutions of the rotor of the synchro resolver 96 theservo-motor 104 will make m revolutions. A suitable pick-off device 108of conventional kind, fitted to the shaft of servo-motor 104, senses therevolutions of that shaft and produces an electrical signal, indicatedby 97A, directly representative of the servo-motor shaft revolutions. Itis found that small errors in the gears at 106 are unimportant sincesuch errors are spread only over one cycle of the transducer gratingpitch and thus are averaged out in the long term over any substantialrange of movement at the transducer. The signal from the servomotorpick-off device and the corresponding number of cycles gone through bythe synchro-resolver therefore can be arranged so as to provide togethera suitable electrical ratio signal which can be applied to accuratemeasurements on gear pairs having a nominal gear ratio of mm For thispurpose two sets of time-phase transducer apparatus of the kindillustrated in FIG. 6 are so arranged that a first set monitors themovement of the first gear wheel of a gear pair under test and a secondset monitors the movement of the second gear wheel, the first wheeldriving the second in the ratio mm. In the first set of apparatus thedrive from the servo-motor 104 to the synchro-resolver is direct, thatis equivalent to a 1:] ratio at the gear box 106; while in the secondset of apparatus the gear box 106 has a ratio n.'m. Thus ences betweenthe read-outs from the two sets of apparatus.

The arrangement of FIG. 1 employing four index gratings with associatedphoto-diodes can be simplified by reduction to two gratings, l6, l8 andphoto-diodes 28, 30, the index gratings being in spatial quadrature onewith the other. The simplified arrangement does not produce quite suchsatisfactory results as that illustrated, because a smaller portion ofthe extended grating 24 is employed at any time, and consequently thereis less scope for elimination of grating error. Further, there is notthe substantial elimination of direct voltages at the input to theamplifiers 38, 40 which is provided by the full inverse parallelconnections illustrated in FIG. 1. i

What I claim is:

1. A time-phase transducer apparatus comprising an extended diffractiongrating, a set of at least two index diffraction gratings each of whichcoacts with part of said extended grating to produce an individual moirefringe pattern, the extended grating and the set of gratings beingcapable of relative movement, a source of cyclically modulated radiationof a given frequency which illuminates the aforesaid gratings to producethe individual moire fringe patterns, the radiation source producing aplurality of radiations of said given frequency but of differentindividual phases for each individual index grating and each indexgrating having an individual phase relationship with the extendedgrating whereby the resulting output arising from each index grating isa plurality of cyclically modulated beams of radiation bearing moirefringe patterns which differ in phase in a cyclically symmetricalmanner, photoelectric transducer means for receiving the resultingoutputs arising from each index grating and combining them to produce atleast one cyclically modulated output signal which in consequence variesin phase in accordance with any relative movement between the extendedgrating and the set of index gratings.

2. Apparatus according to claim 1 in which one radiation source producesa single modulated radiation and n index gratings (where n is at least3) are provided, arranged so that the moire fringe patterns differ fromone another in spatial phase by a whole multiple of l/n of 360.

3. Apparatus according to claim 2 having four index gratings, differingin spatial phase by or multiples thereof, four photo-electric cells forreceiving the outputs from each index grating, a phase shifting circuitto which the photo-electric cells are connected in inverse parallel andwhich imposes relative phase shift of 90 on one input compared with thatimposed on the other input so as to produce an output therefrom whichcontains the modulation frequency of the radiation source and varies inphase with relative movement between the extended grating and the indexgratings.

4. Apparatus according to claim 3 in which the phase shifting circuit isa resistance-capacitance circuit.

5. Apparatus according to claim 1 and having n radiation sources, wheren is at least 3, a corresponding number of index gratings andphoto-electric cells, and oscillator means arranged to modulate theoutputs of the radiation sources so that they differ from one another intime phase by whole multiples of Ur! of 360.

6. Apparatus according to claim 5 and having signal output means whichcomprise a summing circuit to the input of which the outputs of thephoto-electric transducer means are connected so that the output of thesignal output means has substantially the same frequency as themodulation and varies in phase with relative movement between theextended grating and the set of index gratings.

7. Apparatus according to claim 1 said photo-electric transducer meanshaving a single photo-electric cell, signal output means, and focusingmeans intermediate the set of index gratings and the photo-electriccell, arranged so that any resulting output arising from each one of thegratings in the set of index gratings is focused onto the photo-electriccell with the result that the output of the photo-electric transducermeans has substantially the same frequency as the modulation of theradiation source and varies in phase with relative movement between theextended grating and the index gratings.

8. Apparatus according to claim 1 including a synchro-resolver, aphase-sensitive detector, a servomotor and a revolution counter arrangedso that any cyclically modulated output signal is fed to the stator ofthe synchro-resolver, any resulting electrical output signal from therotor of the synchro-resolver is fed to the phase-sensitive detector andis compared therein with a reference signal derived from the modulationwave-form of the radiation source, any error-signal output from thephase-sensitive detector is fed to the servo-motor, which thereupondrives the rotor of the synchro-resolver so as to reduce the electricaloutput signal therefrom towards zero, and the revolution counter recordsany rotary movement of the rotor of the synchro-resolver.

9. Apparatus according to claim 8 including a servoamplifier, in whichany error-signal output from the phase-sensitive detector is amplifiedby said servoamplifier before being fed to the servo-motor.

10. Apparatus according to claim 8 in which the servo-motor drives therotor of the synchro-resolver through a gear box so that the ratiobetween the revolutions made by the servo-motor and the revolutions madeby the rotor of the synchro-resolver is the gear box ratio.

11. Apparatus according to claim 1 in which the extended diffractiongrating is a reflection grating and the source of cyclically modulatedradiation, index gratings and photo-electric transducer means arearranged and adapted so as to cooperate therewith.

0 Q UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,748, 486 Dated July 24, 1973 Inventor(s) Alexander Russell It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

3 Cover page, after item [211 insert -[30] Foreign Application PriorityData December 21, 1970 Great Britain 6048l/70--. Column 6, line 4?,after "imposes" insert --a--.

Signed and sealed this 18th dayof December 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. V RENE D. TEGTMEYER Attesting Officer ActingCommissioner of Patents Patent No. 3,748,486 Dated J ly 24, 1973Inventor(s) Alexander sell It is certified that, error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 45, "produced" should read -produces---. Column 2, line40, "serve" should read --servo-. Column 3, line 39, "l8'" and "20"should read --l8- and --20--, respectively; line 40, "22" shouldread'--22--.

Signed and sealed this 5th day of March 19m.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. A time-phase transducer apparatus comprising an extended diffractiongrating, a set of at least two index diffraction gratings each of whichcoacts with part of said extended grating to produce an individual moirefringe pattern, the extended grating and the set of gratings beingcapable of relative movement, a source of cyclically modulated radiationof a given frequency which illuminates the aforesaid gratings to producethe individual moire fringe patterns, the radiation source producing aplurality of radiatiOns of said given frequency but of differentindividual phases for each individual index grating and each indexgrating having an individual phase relationship with the extendedgrating whereby the resulting output arising from each index grating isa plurality of cyclically modulated beams of radiation bearing moirefringe patterns which differ in phase in a cyclically symmetricalmanner, photo-electric transducer means for receiving the resultingoutputs arising from each index grating and combining them to produce atleast one cyclically modulated output signal which in consequence variesin phase in accordance with any relative movement between the extendedgrating and the set of index gratings.
 2. Apparatus according to claim 1in which one radiation source produces a single modulated radiation andn index gratings (where n is at least 3) are provided, arranged so thatthe moire fringe patterns differ from one another in spatial phase by awhole multiple of 1/n of 360*.
 3. Apparatus according to claim 2 havingfour index gratings, differing in spatial phase by 90* or multiplesthereof, four photo-electric cells for receiving the outputs from eachindex grating, a phase shifting circuit to which the photo-electriccells are connected in inverse parallel and which imposes relative phaseshift of 90* on one input compared with that imposed on the other inputso as to produce an output therefrom which contains the modulationfrequency of the radiation source and varies in phase with relativemovement between the extended grating and the index gratings. 4.Apparatus according to claim 3 in which the phase shifting circuit is aresistance-capacitance circuit.
 5. Apparatus according to claim 1 andhaving n radiation sources, where n is at least 3, a correspondingnumber of index gratings and photo-electric cells, and oscillator meansarranged to modulate the outputs of the radiation sources so that theydiffer from one another in time phase by whole multiples of 1/n of 360*.6. Apparatus according to claim 5 and having signal output means whichcomprise a summing circuit to the input of which the outputs of thephoto-electric transducer means are connected so that the output of thesignal output means has substantially the same frequency as themodulation and varies in phase with relative movement between theextended grating and the set of index gratings.
 7. Apparatus accordingto claim 1 said photo-electric transducer means having a singlephoto-electric cell, signal output means, and focusing meansintermediate the set of index gratings and the photo-electric cell,arranged so that any resulting output arising from each one of thegratings in the set of index gratings is focused onto the photo-electriccell with the result that the output of the photo-electric transducermeans has substantially the same frequency as the modulation of theradiation source and varies in phase with relative movement between theextended grating and the index gratings.
 8. Apparatus according to claim1 including a synchro-resolver, a phase-sensitive detector, aservo-motor and a revolution counter arranged so that any cyclicallymodulated output signal is fed to the stator of the synchro-resolver,any resulting electrical output signal from the rotor of thesynchro-resolver is fed to the phase-sensitive detector and is comparedtherein with a reference signal derived from the modulation wave-form ofthe radiation source, any error-signal output from the phase-sensitivedetector is fed to the servo-motor, which thereupon drives the rotor ofthe synchro-resolver so as to reduce the electrical output signaltherefrom towards zero, and the revolution counter records any rotarymovement of the rotor of the synchro-resolver.
 9. Apparatus according toclaim 8 including a servo-amplifier, in which any error-signal outputfrom the phase-sensitive detector is amplified by said servo-amplifierBefore being fed to the servo-motor.
 10. Apparatus according to claim 8in which the servo-motor drives the rotor of the synchro-resolverthrough a gear box so that the ratio between the revolutions made by theservo-motor and the revolutions made by the rotor of thesynchro-resolver is the gear box ratio.
 11. Apparatus according to claim1 in which the extended diffraction grating is a reflection grating andthe source of cyclically modulated radiation, index gratings andphoto-electric transducer means are arranged and adapted so as tocooperate therewith.